Tools of the above-mentioned type, which are intended for chip-removing machining of foremost workpieces of metal, are usually composed of a carrying or holding basic body, e.g. a cutter head, a drill shank, a turning bar or the like, as well as one or more replaceable cutting inserts, which are mounted in so-called insert seats in the basic body. Most commonly, said insert seat is formed in the basic body itself, but in certain cases it may also be included in a particular shim plate, which in turn is fixed in relation to the basic body. The cutting inserts may have a most varying shape and be indexable in order to enable use of two or more cutting edges included in the cutting insert. Quadrangular or polygonally shaped cutting inserts have at least three or four side support or clearance surfaces, which extend between mutually parallel top and bottom sides of the cutting insert. While the cutting inserts are manufactured from a particularly hard and wear-resistant material, such as moulded and sintered cemented carbide, the basic body is manufactured from a more elastic material, in particular steel.
In order to attain good machining results in respect of precision and surface smoothness of the machined work-piece, it is of great importance that the active edge of the cutting insert gets an exact, predetermined position in relation to the basic body. In many applications, the requirements on dimensional accuracy in respect of the position of the cutting edge in relation to the basic body approaches rather 0.001 mm than 0.01 mm.
Another trend in the development in the technology in question is that cemented carbide inserts already in connection with compression moulding and sintering gets a better and better dimensional accuracy. In order to obtain good precision of the cutting inserts, it was previously necessary to subject the cutting inserts to expensive grinding operations, but by means of improved compression moulding and sintering technique it has, for economical reasons, become more and more interesting to try to get away from the need for precision grinding. However, it is inevitable that today's directly pressed, i.e., not ground cutting inserts, have a dimensional variation of the order of (±)0.5% of the nominal measure of length of the cutting insert. When the cutting inserts are formed with serration connecting surfaces of the type initially mentioned, such dimensional variations result in the position of the cutting insert and thereby of the cutting edge in relation to the insert seat in the basic body being impossible to predetermine in a satisfactory way. In certain cases when the result from the manufacture is good, the cutting edge may end up in the desired position, but when the result is inferior, the position of the cutting edge in relation to the insert seat may deviate to such an extent from the desired position, that the machining precision becomes less good.
In this connection, it should be pointed out that the precision of the ridges in the serration connecting surface forming the insert seat of the basic body always have a good precision, because said connecting surface is produced by chip-removing precision machining, in particular milling, and not by compression moulding/sintering.
Before the introduction of cutting tools having serration connecting surfaces in the interface between the cutting insert and the basic body, the exact position of the active cutting edge was determined by the distance between the edge and the clearance surface positioned on the opposite side of the cutting insert, which clearance surface was pressed against a co-operating support surface in the insert seat. In this case—when said clearance surface formed a reference point that determined the position of the edge—the position precision of the edge could become catastrophically poor if the cutting insert was not ground, because the distance between the active edge and the opposite clearance surface is—in the context—considerable, in particular on large cutting inserts. After the introduction of serration connecting surfaces as means of fixation of the cutting inserts, it has been possible to double the position precision (=the tolerance is halved) of the cutting edge, more precisely by the fact that an intermediate ridge in the serration connecting surface of the cutting insert is selected as reference point for the position of the cutting edge. By the fact that said intermediate ridge is halfway between opposite sides/cutting edges on the cutting insert, the distance is accordingly halved between the active cutting edge and the position-determining reference point, thereby ensuring halving of the tolerance errors. However, also this position precision is unsatisfactory in many of the applications that demand better and better machining results.